Conventionally, refrigeration cycle apparatuses such as air conditioning devices are configured to operate by receiving a supply of a three-phase alternating-current power supply from a commercial power source, a generator, or another source (see, Patent Literature 1, for example). Further, in general, electrical component parts (e.g., a motor of a compressor, a motor of a fan, a solenoid valve, and other elements) constituting a refrigeration cycle apparatus operate by using a three-phase 200-VAC source, a single-phase 200-V AC source, a 12-V DC source, or another power source, as a primary power source thereof. For this reason, refrigeration cycle apparatuses are configured to generate a voltage to be used by electrical component parts from a three-phase 200-V AC source serving as the primary power source and to supply the generated voltage to a refrigerant circuit system thereof.
Further, in a refrigeration cycle apparatus described in Patent Literature 1, a large-capacity inverter device (see Patent Literature 2, for example) is used for driving motors of a compressor, a fan, and other elements. In inverter devices such as the one described in Patent Literature 2, a commonly-used method is a method by which a direct-current bus voltage for driving the inverter is generated by rectifying a three- or two-phase alternating current.
As another example, at data centers and other facilities provided with a large-capacity Information and Communication Technology (ICT) apparatus, there is a trend to significantly improve the efficiency of the system by replacing an alternating-current power supply system with a high-voltage direct-current power supply system (see Non-Patent Literature 1, for example). In such a configuration, it is possible to use the supplied high direct-current voltage as a voltage for driving the inverter device provided in the refrigeration cycle apparatus, without applying any modification thereto. Consequently, it is possible to simplify the configuration of the refrigeration cycle apparatus and to improve the efficiency of the refrigeration cycle apparatus.
Next, a typical configuration of an electrical circuit of an AC-input type refrigeration cycle apparatus (hereinafter, “alternating-current (AC) refrigeration cycle apparatus 1000”) will be explained. FIG. 16 is a circuit diagram illustrating a schematic configuration of an electrical system of the AC refrigeration cycle apparatus 1000. The AC refrigeration cycle apparatus 1000 includes a compressor motor 1030, a DC/AC converter 1021, a smoothing capacitor 1022, a relay unit 1023, a resistor circuit 1024, a three-phase full-wave rectifying circuit 1007, and a zero-cross sensor 1014.
The compressor motor 1030 is configured to drive a compressor (not illustrated).
The DC/AC converter 1021 is configured to drive the compressor motor 1030.
The smoothing capacitor 1022 is configured to smooth an electric current (hereinafter, “current”) supplied to the DC/AC converter 1021.
The relay unit 1023 and the resistor circuit 1024 are configured to suppress an inrush current that may flow from an alternating-current system (hereinafter, “AC system”) into the smoothing capacitor 1022, when power is supplied from an alternating-current circuit breaker (hereinafter, “AC circuit breaker”) 1100.
The three-phase full-wave rectifying circuit 1007 is configured to rectify an alternating current into a direct current.
The zero-cross sensor 1014 is configured to detect the presence of an alternating-current voltage (hereinafter, “AC voltage”).
Next, an operation of the AC refrigeration cycle apparatus 1000 will be explained.
The voltage supplied from an AC system 1300 is taken into the AC refrigeration cycle apparatus 1000 via a system impedance 1011 and the AC circuit breaker 1100. The system voltage taken into the AC refrigeration cycle apparatus 1000 is converted from the alternating current into a direct current by the three-phase full-wave rectifying circuit 1007.
The voltage converted into a direct-current voltage (hereinafter, “DC voltage”) by the three-phase full-wave rectifying circuit 1007 is supplied to the smoothing capacitor 1022 via the relay unit 1023 and the resistor circuit 1024. Further, the direct-current bus voltage smoothed by the smoothing capacitor 1022 is input to the DC/AC converter 1021. In this manner, the AC refrigeration cycle apparatus 1000 drives the compressor motor 1030.
When the power is supplied from the AC circuit breaker 1100, the AC refrigeration cycle apparatus 1000 brings the relay unit 1023 into an open state and slowly charges the smoothing capacitor 1022 by using a small current, from the system via an inrush prevention resistor. Further, when the smoothing capacitor 1022 has been charged with a sufficient amount of DC voltage, the AC refrigeration cycle apparatus 1000 brings the relay unit 1023 into a closed state, so that the DC/AC converter 1021 starts driving the compressor motor 1030.
The commonly-used AC refrigeration cycle apparatus 1000 is provided with a circuit breaker open state determination function to determine the open state of the AC circuit breaker 1100 to prevent an excessive inrush current from flowing therein when the power supply is resumed after the AC circuit breaker 1100 becomes open for some reason during the operation. The AC refrigeration cycle apparatus 1000 is configured so that, when it is determined that the AC circuit breaker 1100 is open, the relay unit 1023 is brought into an open state.
Examples of the circuit breaker open state determination function include a function configured to detect the presence of an AC voltage input to the AC refrigeration cycle apparatus 1000 by using the zero-cross sensor 1014 and to, when the voltage from the AC voltage source has no point crossing zero, determine that no alternating current is present, i.e., that the AC circuit breaker 1100 is open.
As for the AC refrigeration cycle apparatus 1000, by using the circuit breaker open state determination function achieved with the zero-cross sensor 1014, the relay unit 1023 is kept open when the AC circuit breaker 1100 is determined to be open, in response to once becoming open of the AC circuit breaker 1100. With this configuration, it is possible to prevent an inrush current from flowing in, when the AC circuit breaker 1100 becomes closed after that.
Further, in the AC refrigeration cycle apparatus 1000, also when the AC system 1300 experiences an instantaneous voltage drop and the voltage subsequently recovers, a large charging current flows into the smoothing capacitor 1022. However, the AC refrigeration cycle apparatus 1000 is configured so that the system impedance 1011 suppresses the current to some extent. For this reason, by configuring the smoothing capacitor 1022 or another element with an appropriate design, it is possible to avoid an impact that may be made on the AC refrigeration cycle apparatus 1000 by such a large charging current.
Next, a typical configuration of an electrical circuit in a DC-input type refrigeration cycle apparatus (hereinafter, “direct-current (DC) refrigeration cycle apparatus 2000”) will be explained. FIG. 17 is a circuit diagram illustrating a schematic configuration of the electrical system of the DC refrigeration cycle apparatus 2000. The DC refrigeration cycle apparatus 2000 includes a compressor motor 2030, a DC/AC converter 2021, a smoothing capacitor 2022, a relay unit 2023, and a resistor circuit 2024. These elements function in the same manner as the compressor motor 1030, the DC/AC converter 1021, the smoothing capacitor 1022, the relay unit 1023, and the resistor circuit 1024 included in the AC refrigeration cycle apparatus 1000.
To the DC refrigeration cycle apparatus 2000, a DC voltage is supplied via a AC/DC converter 2210 configured to convert the voltage from an AC system 2300 into a direct current and a DC circuit breaker 2100 configured to open and close the direct current. A battery 2220 is installed on the output side of the AC/DC converter 2210. The battery 2220 is provided for the purpose of stabilizing the high-voltage direct current.
Next, an operation of the DC refrigeration cycle apparatus 2000 will be explained.
The voltage supplied from the AC system 2300 is converted into a high-voltage direct current (a direct current of approximately 380 V when a 400-V AC system is used) by the AC/DC converter 2210 and is subsequently taken into the DC refrigeration cycle apparatus 2000 via the DC circuit breaker 2100. The DC voltage taken into the DC refrigeration cycle apparatus 2000 goes through the relay unit 2023 and the resistor circuit 2024 and is further supplied to the smoothing capacitor 2022. Further, the DC voltage smoothed by the smoothing capacitor 2022 is input to the DC/AC converter 2021. In this manner, the DC refrigeration cycle apparatus 2000 drives the compressor motor 2030.
Further, by using the configuration described above, even when the refrigeration cycle apparatus is applied to an air conditioning system for a data center, it is possible, as indicated in Non Patent Literature 1, to reduce power losses because the power corresponding to the one DC/AC converter provided on the uninterruptible power supply device side and the power corresponding to the one AC/DC converter provided on the load side become unnecessary.
In this situation, the battery 2220 not only stabilizes the DC voltage but also serves as a back-up power source when the power supply from the AC system 2300 stops due to a power failure or another cause. However, the output voltage of the battery 2220 varies depending on the charged state (the remaining charge) thereof and, in general, a lowest output voltage is as low as approximately 70% of a highest output voltage. More specifically, when a 400-V AC system is used as the AC system 2300, although the high DC voltage is set to approximately 380 V, the lowest output voltage of the battery 2220 in that situation is approximately 270 V.
In the DC refrigeration cycle apparatus 2000 illustrated in FIG. 17, when the DC circuit breaker 2100 is turned on, the relay unit 2023 operates to suppress the inrush current that may flow from either the AC/DC converter 2210 or the battery 2220 into the smoothing capacitor 2022. More specifically, when the voltage of the smoothing capacitor 2022 is equal to or lower than a predetermined level, the relay unit 2023 is open, and initial charging of the smoothing capacitor 2022 is performed slowly via the resistor circuit 2024. Further, when the voltage of the smoothing capacitor 2022 has reached the predetermined level, the relay unit 2023 is brought into a closed state. With this arrangement, it is possible to prevent the occurrence of losses, because the current flowing for the operation of the compressor thereafter bypasses to flow through the relay unit 2023. In addition, the operation performed when the AC circuit breaker 1100 is turned on in the AC refrigeration cycle apparatus 1000 illustrated in FIG. 16 is also the same.
Also while the DC refrigeration cycle apparatus 2000 is in an operating state, it is necessary to provide a circuit breaker open state determination function to determine the open state of the DC circuit breaker 2100 to prevent an excessive inrush current from flowing therein when the power supply is resumed after the DC circuit breaker 2100 becomes open for some reason.
Examples of the circuit breaker open state determination function used in the DC refrigeration cycle apparatus 2000 include a function configured to determine that the DC circuit breaker 2100 has become open when the voltage of the smoothing capacitor 2022 becomes equal to or lower than an insufficient voltage judgment threshold value Th. The insufficient voltage judgment threshold value Th is set to a value smaller than a lower limit for a tolerated DC voltage. For example, when the DC voltage described above is in the range from 380 V to 270 V, the insufficient voltage judgment threshold value Th is set to a value smaller than 270 V. When the DC circuit breaker 2100 becomes open, because the power keeps being supplied from the smoothing capacitor 2022 to the load, the voltage of the smoothing capacitor 2022 decreases, and after a predetermined period of time has elapsed, it is determined that the DC circuit breaker 2100 is open. In the DC refrigeration cycle apparatus 2000, when the DC circuit breaker 2100 is determined to be open, the relay unit 2023 becomes open, in the same manner as in the AC refrigeration cycle apparatus 1000.